In connection with the construction of industrial switchboards it was previously necessary to include various types of switches in order to meet varying requirements and fulfil various requirements as to loadability, breaking capacity, heat generation etc. The latter applies furthermore when an existing switchboard is to be extended.
Today substantially three different types of switches are employed, viz. conventional quick switches and fuse switches for AC23-operation (motor switches) and parallel switches for AC21 or AC22-operation (load switches). The designations and definitions used are in accordance with the IEC-standard 408.
The above three types of switches were previously delivered completely mounted from the contractors, and as it is impossible for a switchboard constructor to know in advance how many pieces he need of each type of switch (for new switchboards being ordered), it is obvious that great amounts of capital is bound in the stock of switches. In addition, the slightest change of a switch implies usually that the housing is dismounted and that the vital members of the switch are interfered with, i.e. the interior connections to fixed contact locations, the contact bridge, and the guiding mechanism thereof. A typical change is for instance that a fuse switch is altered into a conventional quick switch, or that a motor switch is altered into a load switch. Since such alterations are not allowed by other persons than the contractor partly on account of the safety and partly on account of the product responsibility and the conditions for the fulfilling of the guarantee, the switchboard constructors are thus forced partly to involve a great expensive stock and to put up with delays in case the order involves particular solutions